We have studied the immunostimulatory effects of meningococcal LOS that was tightly associated with outer-membrane proteins (OMP) and undissociable from OMP by sodium deoxycholate treatment. The toxicities of the LOS were greatly reduced when it was tightly associated with the OMP. Immunization of mice with the OMP-associated LOS protected them against experimental meningococcal infection and septic shock. The results have been published. No new research was carried out in this fiscal year. However, we plan to investigate the toxicity and beneficial immunostimulatory effects of detoxified meningococcal LOS and OMP-associated LOS once we obtain the lipid A mutant of Neisseria meningitidis described in our new project on the genetic study of Neisseria meningitidis lipooligosaccharide.